This invention relates to an electrical terminal for connecting a heating grid on a thermal window to a source of electric power. Basically, the invention resides in adapting this structure so that it may be more easily soldered to such a heating grid on a thermal window. By being easily soldered, I mean that the electrical terminal can be soldered to the heating grid in a manner which insures that the electric terminal will be securely bonded to the heating grid and not easily dislodged therefrom if hit by another object. The utility of this electric terminal will become apparent upon further reading of this specification.
The most pertinent prior art that I am aware of includes reissue patent No. 28,295 and U.S. Pat. No. 4,023,008. Both of these patents disclose electric terminals used for connecting a heating grid on a thermal window to a source of electric power. In both of the patents, the electric terminal includes at least one bonding foot which is bonded to the heating grid by means of solder and a lead area to which an electrical connection can be made. In both of the patented structures the bonding feet, identified by the numerals 5 and 6 in Re. No. 28,295, and the numerals 6 and 6a in U.S. Pat. No. 4,023,008, are planar members.
In the normal course of manufacturing of such a terminal, solder is predeposited on the bonding feet. When it is desired to attach the terminal to the heating grid, an operator places the terminal on the heating grid in such a manner that the predeposited areas of solder on the bonding feet are in contact with the heating grid. Thereafter, an operator moves a resistance soldering gun into contact with the bonding feet and energizes the gun so that a current flows through the bonding feet. The current flowing through the bonding feet heats the solder to melt the same and thus causes the bonding of the terminal to the heating grid.
The difficulty with the previous operation has been that in many instances the operator would apply too great a pressure to the resistance soldering gun during the soldering operation. The application of too great a pressure causes two difficulties. The first difficulty is that the application of too much pressure causes a squeezing out of the solder from between the bonding feet and the heating grid resulting in a weakened solder joint. The second difficulty is that the application of too great a pressure generally will cause a dissolution of silver metal which is normally found in the heating grid, which also causes a weakening of the solder joint being formed between the heating grid and the terminal being bonded thereto.
In some instances, the application of pressure to the bonding feet of the terminal during the soldering operation is insufficient and an excessive amount of solder is left at the soldering junction. This excess of solder provides a very weak junction between the terminal and the heating grid. An excessive amount of solder can also cause a canting of the terminal with respect to the heating grid. Either of these conditions mean that the terminal is not securely bonded to the heating grid and may be easily dislodged therefrom if impacted by another object.
The terminal of this invention eliminates the difficulties described above. The operator may press the terminal of this invention with as great a force as he or she desires, but yet the bonding between the terminal and the heating grid will be uniform and will be sufficient to insure the retention of the terminal by the heating grid. The advantages of the structure of this invention will be understood thoroughly after a reading of this specification.